On 05/31/2012 05:04 PM, Glauber Costa wrote:

On 05/30/2012 06:58 PM, jeff.liu-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org wrote:

quoted

Introduce two functions to lock/unlock a particular mount namespace
when container quota operations is performed.

Signed-off-by: Jie Liu<redacted>
---
  fs/namespace.c                |   17 +++++++++++++++++
  include/linux/mnt_namespace.h |   13 +++++++++++++
  2 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index e608199..8823ba8 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c

@@ -2633,3 +2633,20 @@ bool our_mnt(struct vfsmount *mnt)
  {
      return check_mnt(real_mount(mnt));
  }
+
+/*
+ * Lock the mount namespace when performing a particular container
+ * disk quotactl operation, especially to protect removing it.
+ */
+void lock_mnt_ns(struct mnt_namespace *ns)
+{
+    down_write(&namespace_sem);
+}
+
+/*
+ * Unlock the mount namespace after quotactl on that was done.
+ */
+void unlock_mnt_ns(struct mnt_namespace *ns)
+{
+    up_write(&namespace_sem);
+}

diff --git a/include/linux/mnt_namespace.h

b/include/linux/mnt_namespace.h
index 5a8e390..ff72ed5 100644

--- a/include/linux/mnt_namespace.h
+++ b/include/linux/mnt_namespace.h

@@ -9,6 +9,19 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned

long, struct mnt_namespace *,
          struct fs_struct *);
  extern void put_mnt_ns(struct mnt_namespace *ns);

+#ifdef CONFIG_NS_QUOTA
+extern void lock_mnt_ns(struct mnt_namespace *);
+extern void unlock_mnt_ns(struct mnt_namespace *);
+#else
+void lock_mnt_ns(struct mnt_namespace *)
+{
+}
+
+void unlock_mnt_ns(struct mnt_namespace *)
+{
+}
+#endif
+

Seems weird. There is nothing ns-quota specific in locking a namespace.
Also, just grabbing a lock from an outer subsystem is quite ugly. If you
are grabbing a namespace lock, this suggests you are tweaking namespace
data. So you should have that file provide you with a function that does
the full operation.

Maybe this can be safely removed, it is presented like a place holder,
which is suggests to protect changing data inner quota info of a mount
namespace.
However, both quota info initialization and destroy business are all
projected at mount init and put mount namespace stage, so that the
lock/unlock are make less sense here.

Thanks,
-Jeff

Of course there are exceptions to that, but it rings a bell.